I have a user who sent out an email to 4 personal distribution groups and these users are getting duplicate emails up to 15 so far. The personal DL's have company users as well as external contacts. Did some research and saw an article about duplicate emails caused by multiple memberships and DL's expanding on diff exchange servers. However these are personal DL's and assume expansion occurs before it's sent out to the EX server. External contacts as well as internal users are getting duplicates. User reports the interval around every 20 mins. Don't see any issues in the event logs for where the user resides. We don't have message tracking enabled as well so I can't go back to identify if these messages have same message id. Anybody run into this before? Thanks.